The usual - available in Europe but not US
I contacted SRAM as to whether or not they still made the Torpedo 3 thumb shifter for their 3 speed hub... alas, I was informed that: "We currently produce a few shifters that will work with the T3 hub. One is a Dual Drive left hand twist shifter and another is the T3 twist shifter (for right hand). These are available in the US. The thumb (torpedo) style shifter is produced, but isn't imported into the US. To get one of these, you would have to order it from a bike shop in Europe."
Any ideas why the thumb shifter wouldn't have any market in the States?? Bah.